Meeting Abstract
Animals contribute to the management of their physiological fluxes with the environment by building and living in structures such as burrows. Many species of spiders dig burrows, which they close with silk-hinged trapdoors, soil plugs, or a temporary silk webs. Burrow covers are assumed to serve different functions, such as camouflage; barriers against predators, loose soil or flooding; and maintenance of a favorable hydric and thermal environment for the burrow occupant. We investigated the last in wolf spiders (Lycosa sp.) that inhabit loess plains of the Negev Desert, Israel. These, as yet unnamed, lycosids build simple, vertical burrows that reach up to 16 cm in depth and range 0.3-1.7 cm in diameter. When we removed trapdoors from their burrows, the spiders spun webs in their burrow entrances, or alternatively, hid in their burrows until evening. Using fine-gauge thermocouples, we measured a temperature profile that allowed determination of ventilation patterns within the burrows. We found that removing trapdoors increases temperature at the bottom of burrows by ~1 °C at midday in summer. Yet, air from the surface boundary layer did not reach the bottom of the burrows. Direct solar radiation can theoretically reach the bottom of a burrow at midday in summer, based on calculations using natural Lycosa sp. burrow dimensions (n = 181). Partial heating of the burrow walls may drive thermal convection and diffusion in the burrow. However, temperature differences between open and closed burrow are minor, relative to the daily fluctuations in burrow temperatures. Based on experiments with artificial burrows, we conclude that the small size of the burrow entrance, rather than the trapdoor, may play a greater role in maintaining a favorable environment inside the burrow.
